/*
 * Copyright (C) 2015 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef ANDROID_BASE_UNIQUE_FD_H
#define ANDROID_BASE_UNIQUE_FD_H

#include <unistd.h>

// DO NOT INCLUDE OTHER LIBBASE HEADERS!
// This file gets used in libbinder, and libbinder is used everywhere.
// Including other headers from libbase frequently results in inclusion of
// android-base/macros.h, which causes macro collisions.

// Container for a file descriptor that automatically closes the descriptor as
// it goes out of scope.
//
//      unique_fd ufd(open("/some/path", "r"));
//      if (ufd.get() == -1) return error;
//
//      // Do something useful, possibly including 'return'.
//
//      return 0; // Descriptor is closed for you.
//
// unique_fd is also known as ScopedFd/ScopedFD/scoped_fd; mentioned here to help
// you find this class if you're searching for one of those names.
namespace android {
    namespace base {

        struct DefaultCloser {
            static void Close(int fd) {
                // Even if close(2) fails with EINTR, the fd will have been closed.
                // Using TEMP_FAILURE_RETRY will either lead to EBADF or closing someone
                // else's fd.
                // http://lkml.indiana.edu/hypermail/linux/kernel/0509.1/0877.html
                ::close(fd);
            }
        };

        template<typename Closer>
        class unique_fd_impl final {
        public:
            unique_fd_impl() : value_(-1) {}

            explicit unique_fd_impl(int value) : value_(value) {}

            ~unique_fd_impl() { reset(); }

            unique_fd_impl(unique_fd_impl &&other) : value_(other.release()) {}

            unique_fd_impl &operator=(unique_fd_impl &&s) {
                reset(s.release());
                return *this;
            }

            void reset(int new_value = -1) {
                if (value_ != -1) {
                    Closer::Close(value_);
                }
                value_ = new_value;
            }

            int get() const { return value_; }

            operator int() const { return get(); }

            int release() __attribute__((warn_unused_result)) {
                int ret = value_;
                value_ = -1;
                return ret;
            }

        private:
            int value_;

            unique_fd_impl(const unique_fd_impl &);

            void operator=(const unique_fd_impl &);
        };

        using unique_fd = unique_fd_impl<DefaultCloser>;

    }  // namespace base
}  // namespace android

template<typename T>
int close(const android::base::unique_fd_impl<T> &)
#if defined(__clang__)
__attribute__((__unavailable__(
#else
__attribute__((__error__(
#endif
"close called on unique_fd"
)));

#endif  // ANDROID_BASE_UNIQUE_FD_H
